In E-UTRAN system several cell transmission bandwidths are possible, e.g. 1.4 MHz, 3 MHz, 5 MHz, 10 MHz, 15 MHz, 20 MHz, etc. Irrespective of the cell transmission bandwidth a user equipment (UE) is required to perform measurements on the neighbor cells. Hereby, it is important that the measurement reports from different cells are consistent and can be used by the network to execute reliable handovers, i.e. correct handover decisions.
Mobility support is one of the fundamental features of any cellular systems. In E-UTRAN the mobility has to be supported both in idle mode and in connected mode. In idle mode the UE in E-UTRAN shall do autonomous cell reselection based on some network signaled parameters. This allows the network to control UE mobility behavior in the coverage area to some extent.
Furthermore, the UE shall be able to do cell reselection within the same frequency layer (intra frequency cell reselection), between different frequency layers (inter-frequency cell reselection), and also between E-UTRAN and other systems such as UTRAN (inter-RAT cell reselection). In connected mode the network shall direct the UE to perform handover to a particular cell. Though this decision is taken by the network it is generally based on UE measurement reports. As in the case of cell reselection, the UE in connected mode shall also support mobility (i.e. handovers) within the same frequency layer, inter-frequency handovers and inter-RAT handovers. The cell reselection and handovers are generally based on one or more downlink measurements. These measurements are typically done on some known reference symbols or pilot sequences.
Another important aspect of the mobility is the identification of the UE position or geographical location. This allows the UE to get an access to location based services, e.g. map reading. There are several different types of positioning methods. In some of the methods the UE identifies its location based on one or more neighbor cell measurements that are also done on some known channel or pilot sequences.
A neighbor cell measurement is a measurement performed by a UE in serving cell(s) as well as neighbor cells on some known downlink reference symbols or pilot sequences. Unlike other measurements, such as CQI which is done on Transmission Time Interval (TTI) level (e.g. 1 ms), neighbor cell measurements are performed over longer time duration in the order of few 100 ms. The neighbor cell measurements can be broadly divided into two main categories:                Radio-related measurements        Timing-related measurements        
The radio-related measurements are used to take handover decisions and allow UE to do cell reselection in idle mode. A good mobility procedure requires generally more than one measurement since one measurement alone cannot cover all the aspects and criteria. For instance both coverage and load in the cell should impact the cell change decision. In E-UTRAN the measurements are performed on the reference symbols that are sent with a certain pattern defined in time and frequency. This pattern is repeated every TTI (i.e. 1 ms). Some examples of neighbor cell measurements are:                Reference symbol received signal strength indicator (RS-RSSI); it is the same as reference symbol received power (RSRP) defined in E-UTRAN.        Carrier received signal strength indicator (Carrier RSSI)        RS-RSSI/Carrier RSSI; it is the same as reference symbol received quality (RSRQ) defined in E-UTRAN.        
RS-RSSI (or RSRP) is measured over the downlink reference symbol, whereas carrier RSSI is measured over the entire UE reception bandwidth. Furthermore, RSRP is measured per cell whereas carrier RSSI is measured per carrier frequency.
Timing-related measurements are used for time alignment purposes during handover. An example would be the time difference between the reference signals from the serving and target cells. Similarly, other timing-related measurements could be used for positioning. An example is the time difference between the broadcast channel (BCH) from the serving and non-serving cells.
All the neighbor cell measurements are performed over a certain bandwidth. In earlier technologies, such as in WCDMA and GSM, these types of measurements are done over the entire cell bandwidth. One main reason is that in these systems a physical channel is sent over one signal bandwidth in all cells, e.g. 200 kHz in GSM and 5 MHz in WCDMA. On the other hand, in E-UTRAN different cell transmission bandwidths is possible. Therefore an efficient mechanism is needed to get consistent UE reports from different cells even if they operate with different bandwidths.